Among 22 students, 12 play football, 9 play tennis, and 4 play both. One student is chosen at random. What is the probability they play football or tennis, or both?
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Answer: 2217
Count the overlap once: 12+9−4=17.
Probability =2217.
Example 2
Of 30 people, 9 cycle and 12 walk, including 3 who do both. Find P(cycles or walks).
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Answer: 53
Inclusive “or” includes both. Favourable =9+12−3=18. Divide by 30:53.
Example 3
An event occurs 9 times in 30 trials. Estimate its probability from relative frequency.
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Answer: 103
Relative frequency = event count / trial count =309=103.
Put it into practice.
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